Polymerization catalyst

ABSTRACT

Process for preparing a supported Ziegler catalyst by impregnating a magnesium-containing support material with the product of reacting a halogen-containing transition metal compound (other than a fluorine-containing compound) with an aliphatic alcohol under substantially anhydrous conditions. Preferred support materials are magnesium oxide or the product of heating magnesium chloride with silica.

The present invention relates to a supported Ziegler polymerisationcatalyst and to the use of the catalyst in the polymerisation of1-olefins.

It has long been known that olefins such as ethylene can be polymerisedby contacting them under polymerisation conditions with a catalystcomprising a transition metal compound, e.g. titanium tetrachloride anda co-catalyst or activator, e.g. an organometallic compound such astriethyl aluminium. Catalysts of this type are generally referred to asZiegler catalysts and will be referred to as such throughout thisspecification. The catalyst and co-catalyst together will be referred toas activated Ziegler catalysts. The deposition of such catalysts onsupport materials such as silicon carbide, calcium phosphate, magnesiumor sodium carbonate is also known. UK patent specification No. 969,764discloses a catalyst of the supported Ziegler type comprising (a) theproduct of reaction carried out in an inert liquid hydrocarbon undercertain conditions between a halide or oxyhalide compound of a groupIVa, Va, VIa, metal of the Periodic System, .[.Mandeleev's.]..Iadd.Mendeleev .Iaddend.version, and a dry (as therein defined), finelydivided particulate inorganic oxide other than silica, alumina oralumina-silica having an average particle size of less than 1 micron andhaving surface hydroxyl groups thereon, and (b) (as co-catalyst) anorganometallic compound or a metal hydride as therein defined. Examplesof suitable inorganic oxides are said to be titania, zirconia, thoriaand magnesia.

It is an object of the present invention to provide an improvedsupported Ziegler catalyst.

Accordingly the present invention provides a process for the productionof a supported Ziegler catalyst comprising impregnating amagnesium-containing support material with the product of reacting ahalogen-containing transition metal compound other than afluorine-containing compound with an aliphatic alcohol undersubstantially anhydrous conditions.

The magnesium-containing support material can be, for example, magnesiumoxide, magnesium hydroxide, magnesium chloride, magnesium bromide,magnesium iodide, magnesium hydroxy chloride, magnesium carbonate,hydrated magnesium halides, magnesium salts of organic acids or calcinedmagnesium salts, for example calcined magnesium chloride or oxalate.Preferred magnesium-containing support materials are magnesium oxide;and the product of heating together anhydrous magnesium chloride and asilica support at a temperature in the range 150°-1,000° C. Magnesiumoxide is particularly preferred. Grades of magnesium oxide that can beemployed in the present invention preferably have a particle sizegreater than 0.01 micron, for example 0.01 to 500 microns, mostpreferably 1 to 100 microns. Magnesium oxide having a surface area inthe range 1 to 1,000 square meters per gram and a hydroxyl content <0.2OH groups per magnesium atom is particularly preferred. It is preferredto employ magnesium oxide that has been obtained by the thermaldecomposition of magnesium hydroxide although magnesium oxides obtainedby for example thermally decomposing magnesium carbonate, magnesiumnitrate or basic magnesium carbonate or by combustion of magnesium metalare also suitable.

The halogen-containing transition metal compound must react with thealiphatic alcohol under the reaction conditions employed. Hydrogenhalide is formed during the reaction and this may be evolved as gaseoushydrogen halide, or remain in solution if the reaction is carried out insolvent or with excess alcohol, or the hydrogen halide may form acomplex with the reaction product. The halogen-containing transitionmetal compound is suitably a halogen containing compound of a metal ofgroups 4A, 5A or 6A of the Periodic Table .[.(Mendeleef).]..Iadd.(Mendeleev).Iaddend.. Examples of suitable compounds are halides,halo-alkoxides or oxyhalides of titanium vanadium, zirconium andchromium or mixtures thereof. Preferred halogen-containing transitionmetal compounds are those having the general formula Ti(OR)_(n) Cl_(4-n)wherein 0≦n<4 and R is a hydrocarbon group, preferably an alkyl groupcontaining 1-6 carbon atoms. Most preferably n has any value from 0 to 3inclusive. Examples of preferred transition metal compounds are TiCl₄,Ti(OC₂ H₅)Cl₃, Ti(iOPr)Cl₃, ZrCl₄ and VOCl₃ or mixtures thereof.

The quantity of halogen-containing transition metal compound employed issuitably at least sufficient to give a concentration of transition metalin the final catalyst in the range 0.1 to 30%, preferably 0.5 to 15%,most preferably 1 to 7% based on the total weight of catalyst. Ifdesired, an excess, for example up to 100 times the concentration in thefinal catalyst, of halogen-containing transition metal compound may beemployed provided that the final catalyst contains 0.1 to 30% oftransition metal.

The aliphatic alcohol employed in the present invention is suitably astraight or branched chain alcohol containing up to 12 carbon atoms,preferably 1 to 6 carbon atoms for example methanol, ethanol,isopropanol and isobutanol.

The quantity of alcohol employed is suitably 0.1 to 4.0 moles,preferably 1.0 to 3.5, most preferably 1.5 to 3.0 moles per mole oftransition metal compound.

The impregnation of the magnesium containing support material can becarried out for example by reacting the halogen-containing transitionmetal compound with the aliphatic alcohol in the presence of themagnesium-containing support material. Alternatively thehalogen-containing transition metal compound and the aliphatic alcoholcan be reacted together and then added to the magnesium containingsupport material.

The reaction between the halogen-containing transition metal compoundand the aliphatic alcohol is preferably carried out in the presence ofan inert solvent, examples of suitable solvents being hexane,cyclohexane, isobutane, isopentane, toluene and mixed aliphatic andaromatic hydrocarbon solvents. The reaction can be carried out at anydesired temperature. Normally temperatures in the range 0°-150° C. arefound to be satisfactory.

The impregnation of the magnesium-containing support material ispreferably carried out at a temperature in the range 0° to 240° C., mostpreferably in the range 40° to 140° C. The impregnation can be carriedout in the presence of an inert diluent or a solvent for the reactionproduct of the halogen-containing transition metal compound and thealcohol. Suitable inert diluents (which in some cases are also solventsfor the said reaction product) are, for example, saturated aliphatichydrocarbons such as petroleum ether, butane, pentane, hexane, heptane,methyl cyclohexane and aromatic hydrocarbons such as benzene, tolueneand xylene. When an inert diluent or solvent is employed it is oftenconvenient to carry out the impregnation of the magnesium-containingsupport material at the reflux temperature of the solvent.

Any excess transition metal compound remaining in the catalyst after theimpregnation (i.e. transition metal compound that has not reacted withor not been absorbed by the support material) is preferably removed fromthe catalyst, for example by solvent washing, filtration, centrifugingor other convenient techniques which do not have a deleterious effect onthe catalyst.

All stages of the catalyst preparation are preferably carried out in theabsence of moisture.

The present invention further provides a process for polymerising1-olefins comprising contacting, under polymerisation conditions, themonomeric material with the supported Ziegler catalyst of the presentinvention in the presence of a Ziegler catalyst activator.

The polymerisation process according to the present invention can beapplied to the polymerisation of 1-olefins e.g. ethylene or propylene ormixtures of olefins, e.g. ethylene with other 1-olefins, for example,propylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene-1,1,3-butadiene or isoprene. The process is particularlysuitable for the polymerisation of ethylene or copolymerisation ofethylene with up to 40% weight % (based on total monomer) of comonomers,i.e. one or more other 1-olefins.

As in the case with other supported Ziegler catalysts the catalyst ofthe present invention must be activated with a Ziegler catalystactivator. Ziegler catalyst activators and the methods by which they areused to activate Ziegler catalysts are well-known. Examples of Zieglercatalyst activators are organic derivatives or hydrides of metals ofGroups I, II, III and IV of the Periodic Table. Particularly preferredare the trialkyl aluminiums or an alkyl aluminium halide, e.g. triethylor tributyl aluminium.

The polymerisation conditions can be in accordance with known techniquesused in supported Ziegler polymerisation. The polymerisation can becarried out in the gaseous phase or in the presence of a dispersionmedium in which the monomer is soluble. As a liquid dispersion mediumuse can be made of an inert hydrocarbon which is liquid under thepolymerisation conditions, or of the monomer or monomers themselvesmaintained in the liquid state under their saturation pressure. Thepolymerisation can, if desired, be carried out in the presence ofhydrogen gas or other chain transfer agent to vary the molecular weightof the produced polymer.

The polymerisation is preferably carried out under conditions such thatthe polymer is formed as solid particles suspended in a liquid diluent.Generally the diluent is selected from paraffins and cycloparaffinshaving from 3-30 carbon atoms per molecule. Suitable diluents include,for example, isopentane, isobutane, and cyclohexane. Isobutane ispreferred.

The polymerisation can be carried out under continuous or batchconditions.

Methods of recovering the product polyolefin are well-known in the art.

The polymerisation catalyst of the present invention can be used to makehigh density ethylene polymers and copolymers at high productivityhaving properties which render them suitable for injection moulding. Thecatalysts have a high activity and are capable, under particle formprocess conditions, of producing polymers having a commercially usefulparticle size distribution.

The invention is further illustrated by the following examples:

In the Examples the melt index (MI₂.16) and high load melt index MI₂₁.6)were determined according to ASTM method 1238 using 2.16 kg and 21.6 kgloads respectively; the units are grammes per 10 minutes.

EXAMPLE 1

A magnesium oxide known as Maglite D, supplied by Plastichem Ltd.,Esher, Surrey, England and manufactured by thermal decomposition ofmagnesium hydroxide was dried under a pressure of 100 mm Hg at 150° C.for 1.5 h, then cooled to room temperature in a desiccator.

150 ml dry cyclohexane and 57 ml isoproponal were added to a flask whichhad been flushed out with dry nitrogen. 36.4 ml titanium tetra-chloridewas added slowly with stirring and the mixture was heated under refluxfor 0.5 h at which stage some, but not all of the HCl produced had beenboiled off. The product is believed to be a complex of Ti(OPr^(i))₂Cl₂,, HCl and excess Pr^(i) OH. 10 g of the dry magnesium oxide was thenadded and the mixture heated under reflux for a further 4 h. Aftercooling, the catalyst was washed six times with cyclohexane (150 mlaliquots) by which time the concentration of titanium in the wash liquorwas less than 1 g/liter. The catalyst was stored under nitrogen and usedas a slurry in cyclohexane.

The polymerisation was carried out in a 2 liter stainless steel stirredreaction vessel. The solid catalyst was added as a slurry in cyclohexaneto the reactor purged with inert gas and maintained at 60°-75° C.Isobutane (1 liter) containing aluminium triethyl was then added and themixture brought up to reaction temperature. Hydrogen (60 psi) was addedand the total pressure was brought up to 600 psi by the addition ofethylene. Ethylene was added continuously to maintain this pressure asthe reaction proceeded. The results are recorded in the Table.

EXAMPLE 2

A grade of magnesium oxide known as Maglite K (10 g) was slurried in 100ml dry cyclohexane containing isopropanol and charged to a nitrogenpurged reaction vessel. 12.2 ml TiCl₄ was added slowly from a droppingfunnel. The mixture was refluxed for 2 hours during which time some HClwas boiled off, although part remained associated with the produced.[.Ti(OPr^(i))₂ CL₂ .]. .Iadd.Ti(OPr^(i))₂ Cl₂ .Iaddend. and excessPr^(i) OH.

The catalyst was washed with 150 ml aliquots of cyclohexane to removeunreacted titanium compounds until the titanium level in the washingswas <1 g/liter, and stored under nitrogen.

Polymerisation was carried out as for Example 1; the results are givenin the Table.

EXAMPLE 3

31.7 g ZrCl₄ were mixed with 37.8 g TiCl₄ in a nitrogen purged glovebox. 100 ml dry cyclohexane were added followed by 44.8 g isopropanolfrom a dropping funnel. The mixture was refluxed for 1/2 hour duringwhich some, but not all of the produced HCl was boiled off. 10.9 g MgO(Maglite K, Plastichem Ltd., Esher, Surrey) was added in the form of aslurry in 50 ml dry cyclohexane. The mixture was refluxed for a furtherhour. The catalyst was then washed with 150 ml aliquots of freshcyclohexane to remove unabsorbed transition metal compounds and wasstored in a dry nitrogen atmosphere. Polymerisation was carried out asfor Example 1; the results are given in the Table.

EXAMPLE 4

6.3 ml of VOCl₃ was added to 29.2 ml TiCl₄ in a dropping funnel andadded slowly to a stirred, nitrogen purged mixture of 57.0 mlisopropanol in 100 ml cyclohexane. A precipitate formed and wasdissolved by heating the mixture to around 60° C. 10.0 g Maglite K MgO(Plastichem Ltd., Esher, Surrey) was added in the form of a slurry in 50ml dry cyclohexane and the mixture heated under reflux for 3 hours. SomeHCl boiled off but the rest remained associated with the mixture. Thecatalyst was washed with fresh cyclohexane (150 ml aliquots) to removeunreacted transition metal compounds. The catalyst was stored undernitrogen as a slurry in cyclohexane.

Polymerisation tests were carried out as for Example 1; the results aregiven in the Table.

                                      TABLE                                       __________________________________________________________________________     Wt. (g)      H.sub.2 Partial                                                                      Reaction                                                                             Run Length                                                                           Wt. Polymer                                Example                                                                            Catalyst                                                                           AlEt.sub.3                                                                        Pressure (psi)                                                                       Temp. (°C.)                                                                   (min)  (g)    MI.sub.2.16                                                                       MI.sub.2.16 /MI.sub.21.6        __________________________________________________________________________    1    0.085                                                                              0.167                                                                             60     86     40     489    3.2 24                              2    0.098                                                                              0.167                                                                             60     92.0   60     448    2.1 25                              3    0.112                                                                              0.334                                                                             80     84.0   60     259    1.5 26                              4    0.043                                                                              0.167                                                                             60     89.5   60     241    0.48                                                                              28                              __________________________________________________________________________                           Sieve Analysis (% w/w of Polymer)                                        Example                                                                            >1000μm                                                                          1000-500μm                                                                        500-250μm                                                                        250-106μm                                                                        <106μm                     __________________________________________________________________________                      1    18.6  60.8   20.2  0.4   0.0                                             2    11    47     38    4     1                                               3    1     18     46    33    1                                               4    41    48     6     4     1                             __________________________________________________________________________

We claim:
 1. A process for the production of a supported Zieglercatalyst component comprising reacting a transition metal compound whichis a chloride, chloro-alkoxide or oxychloride of titanium, vanadium orzirconium, with an aliphatic alcohol containing 1-6 carbon atoms andimpregnating a magnesium oxide support material .Iadd.having an hydroxylcontent of less than 0.2 OH groups per magnesium atom .Iaddend.with theproduct of said reaction, said reaction and impregnation being carriedout under substantially anhydrous conditions.
 2. Process according toclaim 1 wherein said support material is magnesium oxide prepared by thethermal decomposition of magnesium hydroxide.
 3. Process according toclaim 1 wherein said transition metal compound has the general formula.[.Ti(OR)_(n) CL_(4-n) .]. .Iadd.Ti(OR)_(n) Cl_(4-n) .Iaddend. wherein nhas any value from 0 to 3 inclusive and R is an alkyl group containing1-6 carbon atoms.
 4. Process as claimed in claim 1 wherein saidtransition metal compound is TiCl₄.
 5. Process as claimed in claim 1wherein said aliphatic alcohol is methanol, ethanol, isopropanol orisobutanol.
 6. Process as claimed in claim 1 wherein the quantity ofhalogen-containing transition metal compound employed is at leastsufficient to give a transition metal concentration in the finalcatalyst in the range 0.5 to 15% based on the total weight of catalyst,and the quantity of aliphatic alcohol employed is in the range 0.1 to4.0 moles per mole of halogen-containing transition metal compoundemployed.
 7. A process for the production of a supported Zieglercatalyst comprising impregnating a magnesium oxide support material.Iadd.having an hydroxyl content of less than 0.2 OH groups permagnesium atom .Iaddend.with the product of reacting togetherisopropanol and titanium tetrachloride under substantially anhydrousconditions.